In the late-1950s the young Michael Caine appeared in Cross's first play, One More River, at the Liverpool Playhouse; Laurence Olivier subsequently presented the play in London's West End in 1959 (sans Michael Caine, although Robert Shaw played another role in the play).
In 1960 Maggie Smith was cast in the West End production of Cross's second play, Strip the Willow. The actress gave a career-launching performance -- and the playwright fell deeply in love with his star,making plans to divorce his first wife, Elizabeth Clunies-Ross.
In a twist of events as dramatic as any play, Maggie Smith then fell in love with and married Robert Stephens -- and Cross, while working on the screenplay of Lawrence of Arabia, married the model Gayden Collins.
When the rocky Smith-Stephens marriage ended in divorce in the mid-'60s, Cross ended his second marriage and married Smith. Dame Maggie often said in interviews that Cross was the "rock" of her life.
Cross also wrote the librettos to two operas by Richard Rodney Bennett (The Mines of Sulphur and Victory) and the book for the '60s musical Half a Sixpence, starring Tommy Steele.
His last work for theatre was an adaptation of The Scarlet Pimpernel, directed by Nicholas Hytner and starring Donald Sinden, which played at Her Majesty's Theatre in London in 1985.
Cross is survived by Maggie Smith and two stepsons -- the actors Chris Larkin and Toby Stephens.
--By Rebecca Paller